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The Disease Prevention Illusion: A Tragedy in Five Parts

The views expressed are those of the author and are not necessarily those of Scientific American.

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Cartoon of an early bird catching no wormsAct I: An ounce of “prevention.”

“Prevention is better than cure.” Aphorisms like this go back a long way. And most of our dramatic triumphs against disease come from prevention: clean water, making roads and workplaces safer, antiseptic routines in hospital, reducing smoking, immunization, stemming the spread of HIV.

Many of our cultural superstitions and greatest feats of gullibility are in the name of prevention, too. Of course. We generally have a pretty fervent desire to believe in human actions that can prevent the cruelties of fate. The fear of death eats logic for breakfast.

It’s ironic really. The lure of prevention is freedom from disease. But it has become a key driver of over-medicalization of our lives and a growing shadow of disease angst when we’re the healthiest generation the world has ever seen.

Act II: We’re so lucky they caught it early…

Ignoring symptoms, not knowing you’ve got a dangerous infectious disease, and being too fatalistic about seeking help – these are recipes for disaster. But we tend to portray earliness as if it’s always a virtue, though, and that can be a trap, too.

Why? Because while we can be too late for anything to help, we can also be too early to make a difference for the better. That might not sound like a problem. But it can be.

Sketch of lead-time bias

Lead-time bias: How early detection shifting the diagnosis needle can lengthen "disease survival rate" without lengthening life

Some diseases and conditions have a long lead time, developing so slowly, they may never actively threaten our health. When we’re diagnosed early with those, we’ve “had” the disease for longer, but we don’t live longer. All we’ve done is increase our “disease survival” by shortening the “disease-free” part of our lives.

Lead-time bias leads to a wildly misleading use of survival statistics. Even most doctors fall into this statistical trap. It has a lot to do with why early detection so often fails to deliver on the dramatic benefits some expect.

Believing in the benefits of being early without good evidence, isn’t confined to just disease. It’s true of early intervention with children. Dorothy Bishop explains what this means for children with slower than average reading development for example – and Jon Brock discusses the same phenomenon with a theory about detecting autism in babies.

Act III: Screening and the triumph of hope over reason.

Only some screening does good – and it can always do harm. That’s about the reverse of what many people would like to be true.

We’ve just seen one reason that can mislead people – lead-time bias. But there are other phenomena that can exaggerate the benefits: the healthy volunteer effect, for example. Exactly the people who could least benefit from screening, tend to use it more. And they have better outcomes because they were always going to, regardless.

Cartoon of reading rights at screening

Screening has to help more people than those who would have been diagnosed anyway when symptoms were being investigated. And there has to be a test that’s accurate enough and acceptable enough for widespread use. And there has to be effective treatment that can make a difference if it’s used before there are symptoms.

There’s a double whammy here. Those people who fall into the logical fallacy of thinking, “her doctor found cancer after those symptoms,” therefore “I should be screened” – instead of “I should take symptoms seriously.” And those who ignore symptoms, because they were screened and believe they’re in the clear.

When early intervention fails to halt disease progression, there’s also a trend for some doctors to try to intervene even earlier. Perhaps even screening for “pre-disease.” While it’s possible that sometimes will pay dividends, this is generally grasping at straws. More often than not, we can expect this to be what I call “the pre-disappointment phase.”

Act IV: All’s fair in love and the ideological prevention wars.

There is a science to evaluating the effects of screening tests. There’s a good introduction here. So you’d think that questions about what screening programs are worthwhile could be sorted out.

Cartoon about the power of one anecdote

But the emotional stakes are high when it comes to preventing disease. And many people have become so vested in ideological camps about screening, that they’ve basically become pro- or contra- screening fundamentalists.

Unfortunately, that’s as true of some scientists in the field as it is of other partisans. Michael Marmot is the professor who led an independent panel in the UK through the mammography minefield. He wrote, “people interpret evidence and, indeed, influence its generation. Judgments often reflect more about starting assumptions than they do about the nature of the evidence…[O]ne only has to look at the author of an article to make a reasonable guess whether it will be pro or con.”

If you’d like to catch up on the multiple meta-analyses about screening for breast cancer with mammography, I’ve summarized them here on PubMed Commons.

Act V: The suffering of the over-diagnosed and the spreading cloud of disease angst.

The tragedy of the disease prevention illusion carries a heavy toll. First, there are many people who may benefit most from prevention interventions, but can’t take advantage of ways to improve their life chances. Resources may even be diverted from them because of the increase in diagnoses of others – something Margaret McCartney calls “the patient paradox” and Julian Tudor-Hart dubbed “the inverse care law.” What’s more, the constant bombardment with fearful messages may even backfire.

Cartoon of Public Service Announcement on Disease De-Awareness Day

Then there are the swelling numbers of people who are over-diagnosed, fighting heroic battles with disease phantoms and toxic, mutilating treatments that were never necessary. As the numbers of people being diagnosed with serious diseases grow, the chances we’re affected, or someone we know and love is affected, grow too. And the shadow of fear of disease spreads.

Most of the time we just can’t know what would have happened if…. That doesn’t reduce the feeling of having dodged fate’s sword, though. And the chance that we, or someone we know, are “living proof” of the benefits of early detection makes it hard to get this into perspective. Widening the pool of people who understand and communicate the complexities of clinical effectiveness research with clear view to minimizing their own biases as well seems to me essential.

“An ounce of prevention is worth a pound of cure.” We’ve recognized the false expectations we inflate with the fast and loose use of the word “cure” and usually speak of “treatment” instead. We need to be just as careful with the P word.


Cartoon faceBrowse through all my posts at SciAm on prevention-related themes.

The recommendations of the US Preventive Services Task Force and more information about them is here.

Find out more about preventing over-diagnosis here.

Here’s a more technical primer about bias in finding disease.

The 1968 World Health Organization report by Wilson and Jungner that codified the principles of screening for disease is here.

The Statistically Funny cartoons are my original work (Creative Commons License).


* The thoughts Hilda Bastian expresses here at Absolutely Maybe are personal, and do not necessarily reflect the views of the National Institutes of Health or the U.S. Department of Health and Human Services.

Hilda Bastian About the Author: Hilda Bastian likes thinking about bias, uncertainty and how we come to know all sorts of thing. Her day job is making clinical effectiveness research accessible. And she explores the limitless comedic potential of clinical epidemiology at her cartoon blog, Statistically Funny. Follow on Twitter @hildabast.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. Carolyn Thomas 9:53 am 03/24/2014

    Brilliant. Brilliant. And Brilliant!

    And did I mention BRILLIANT?!?

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  2. 2. Claudelle 8:00 pm 03/24/2014

    It’s not, as this author states, that prevention “has become a key driver of over-medicalization of our lives.” because what the medical industry calls preventive interventions (eg mammography) has nothing to do with prevention of disease but with detection of disease, and subsequent treatment. The medical establishment, a profit-driven business, does those things that make them money. Calling screening test preventive procedures is little more than marketing propaganda, promoting their products to the public. Little good science supports these tests, while it is mostly the claims of the medical authorities that do. Eg, a large volume of meaningful evidence irrefutably supports the notion that mammography is mostly ineffective but seriously harmful to most women (source: The Mammogram Myth by Rolf Hefti).

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  3. 3. Hilda Bastian in reply to Hilda Bastian 8:37 pm 03/24/2014

    Thanks, Carolyn! So glad you liked it.

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  4. 4. Hilda Bastian in reply to Hilda Bastian 8:54 pm 03/24/2014

    Claudelle, I very much disagree. The link with my statement there (which I’m adding again here) related to holistic medicine. By no means were my comments related only to early detection – and my conclusion in the post was specifically critical of the way the word “prevention” is used. There we would agree: using the word “prevention” when it’s early detection of disease, or precursors of disease, or using “prevention” when it’s about reducing risks rather than eliminating the potential, is what I was aiming to criticize there.

    The conventional “medical industry” as you describe it does not equate prevention only with secondary prevention or early detection. Immunization, accident prevention, containing infectious disease, controlling blood pressure (which itself is not a disease) to prevent stroke – there is a great deal of reducing the risk of disease developing, and even of preventing it entirely, in “establishment” medicine.

    Other parts of health care than the medical establishment also make profits – and can indeed be very lucrative. And the same criticisms apply there. A naturopath selling vitamins or other remedies and arguing that I should be mindful of many aspects of the way I live my life daily in order to prevent disease, is medicalization too as far as I’m concerned. That’s the point I was making by referring to the link about holistic medicine encroaching on the whole of life. The selling of dietary supplements (all of which make profits, and some of which may cause harm) and many other prescriptions and proscriptions that intrude on your diet, the way you are supposed to think, the way you are supposed to move, and the way you are supposed to feel, are medicalization – even if the medical tradition involved is not the medical establishment.

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  5. 5. AndrewK999 7:53 am 03/25/2014

    If current screening methods are ineffective in reducing mortality, doesn’t that simply mean that our current methods are of poor quality?

    Focusing on breast cancer screening for example, I read the aforementioned Cochrane review of mammography and the main concerns, in terms of human cost were alarmingly high false-positive rates (not to mention false-negatives), over-treatment of cases that would not lead to morbidity or mortality and the overall invasiveness of the procedure.

    The invasiveness of the procedure itself is (I believe) an artefact of out-dated imaging technologies – in the past they relied on film.
    With digital imaging technology, it is in principle possible to do such imaging without ‘parallel plate compression’, though it requires a large amount of data to be captured in a very small amount of time (large computational demands).

    Perhaps the key message is not to reject the idea of screening, but reject it for now to send a message to those who are developing or pushing such screening to go back to the drawing board and develop higher quality and more human friendly methods before bringing it to the masses. Along with better training and education of physicians to avoid over-diagnosis.

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  6. 6. Hilda Bastian in reply to Hilda Bastian 11:38 pm 03/25/2014

    AndrewK999, I don’t know that better technology is always going to be the answer – any more than screening ever earlier is going to be. It may well be, in some circumstances. However, being able to know whether potential precursors will remain dormant or become threatening to health or life could often be more complicated. And it may not just be a function of the limitations of imaging technology.

    There are screening programs that are effective at reducing the risk of dying from particular diseases – it’s just that it’s not an easy thing to achieve. I don’t know whether you read my comments on the Cochrane review about mammography, but I found the data analyses and conclusions of other reviews more convincing.

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  7. 7. AndrewK999 1:49 am 03/26/2014

    I think the point is that we need to keep an open mind – we shouldn’t assume that screening is automatically effective, nor that it cannot be effective, but to continue to examine it to improve effectiveness and lower harms. Then only roll it out on a large scale once it is proven to be beneficial.

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  8. 8. gkromer 12:09 pm 03/26/2014

    This article is about prevention defined as “tests” but what about prevention defined from the patient’s point of view as “taking care of your body and continuously learning how to do that better.” My blog post “Let’s Rediscover Preventive Health Care,”

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  9. 9. Hilda Bastian in reply to Hilda Bastian 8:10 am 03/27/2014

    I did concentrate a fair bit on identifying disease, gkromer, but I didn’t limit it to that. There are many prescriptions and proscriptions, as I said at the outset. The issues of hope/belief over proof apply. A lot of that which people would like most fervently to be true, isn’t necessarily. Major life changes in the name of disease prevention, like quitting smoking, can prevent disease. But many do not. To live a certain way as a medical intervention is itself, I believe, as I said, a major piece of medicalization and intrusion. We are bombarded with people telling us how to live. I would encourage people to take the time to read this article by Marc Girard, and consider what the implications are of claims about how to live, if they are not supported by very strong evidence indeed.

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  10. 10. gkromer 9:02 pm 03/27/2014

    Many people do not have good information about the consequences of the decisions they are making about diet and exercise. Doctors’ offices are too busy to provide these facts.

    What about choosing to live a certain way because it makes your feel good? As I’ve gotten into better shape physically, I’ve had more confidence to say “no” to medical interventions that seem worthless or even harmful.

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  11. 11. Hilda Bastian in reply to Hilda Bastian 12:57 pm 03/28/2014

    Gkromer – totally! That’s wonderful. What makes one person feel good, though, won’t necessarily do the same for someone else, is all.

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  12. 12. MTomasson 3:06 pm 03/28/2014

    Largely sympathetic to your points..but…
    “we’re the healthiest generation the world has ever seen.”
    Really? If we’re so healthy, why are we spending astronomical sums of money on medical care?

    Do you disagree with the thought that decreased colon cancer rates over the past 10 years are due to screening?

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  13. 13. Hilda Bastian in reply to Hilda Bastian 6:23 pm 03/28/2014

    I agree that colon cancer screening is one of the effective screening programs, MTomasson. We’re the healthiest generation the world has ever seen? Yes, really. See Hans Rosling’s summary. We don’t spend astronomical sums of money on medical care because our populations are sicker than those in the past. It’s a question of privilege – and it’s astronomical because society is willing to pay that and so on. There’s no way we need it all, that’s for sure – and some of it makes us sicker. It’s a big and interesting question, why, as we’ve been less threatened by early death, we’ve become more scared of it. It’s part of our faith in technology as a society, and many other things, isn’t it?

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  14. 14. Catharine 10:55 pm 03/30/2014

    Brilliant – I’ve been waiting for something like this. As other commentators note, preventive medicine isn’t really preventive. At best, it offers risk reduction or early detection. I recommend Gilbert Welch’s book, OverDiagnosis, and Barbara Roberts’s book, The Truth About Statins. These authors are on faculty at Dartmouth and Brown respectively.

    Re the point about colon cancer, the 30% reduction in deaths over 35 years is misleading. Let’s just take women (from data reported in the WSJ based on the CDC)
    In 1975, 20/100,000 women over 50 died over colon cancer; today it’s 13.3/100,000. That’s a reduction of 6.7/100,000 or .007 percent or one out of about 14,500.

    In another study WSJ 2/23/2012:
    In a study of about 2600 people who had a colonoscopy 1980-1990, 12 died from colon cancer. This number compares with 25.4 colon cancer deaths among 2600 people in the general population. The reports glowingly talk about a 50% reduction in deaths; actually the reduction is about 13.5/2600 or .05%.

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  15. 15. Hilda Bastian in reply to Hilda Bastian 7:53 am 04/1/2014

    Thanks, Catharine!

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  16. 16. EEBAust 8:45 am 04/2/2014

    This sort of article gives me hope, far too many people have been harmed by screening and very few have given informed consent. (in many cases there is no consent at all, i.e. you need a pap test for the Pill, not true, do men need a colonoscopy for Viagra?)
    I often wonder how we got so far away from ethical cancer screening in women’s screening programs, pap testing was started with no randomized controlled trials and has been horribly over-used resulting in huge over-treatment rates. (for no additional benefit to women) The evidence is ignored in favour of excess.
    Screening has also, become a mandate for women, the attitude is: you must screen. Many women are coerced into screening to get the Pill or even non-emergency medical care. It’s an oppressive climate that silences, misleads and manipulates women.

    If you compare the pap testing programs in The Netherlands and Finland they are in sharp contrast to Australia and the States, the former are based on evidence, the latter countries…excess is the norm.
    Australia thankfully, no longer recommends the routine breast and pelvic exam, but horribly over-screens with the pap test so we have huge excess biopsy/over-treatment rates. Almost all of this damage is avoidable.
    The new Dutch program will scrap population pap testing, 5 yearly from 30 to 60, and offer instead 5 HPV primary tests or women can self-test with the Delphi Screener, at ages 30,35,40,50 and 60 and ONLY the roughly 5% who are HPV+ will be offered a 5 yearly pap test. Most women are having unnecessary pap tests.
    The new Dutch program will save more lives and takes most women out of pap testing and harms way. Of course, this means the loss of a small fortune for vested interests and so change will be challenged. “we’re concerned women will die”, “this is about cost-cutting”.etc…most women are in the dark so it’s hard to make an informed decision and they end up screening through pressure, having been misled, scared, manipulated or because they think they “have to screen” etc.
    Many women now fear their asymptomatic body and hand them over to the medical profession, they have no trust, their body is “pre-cancerous”, a ticking time bomb.

    I’m 56 and have never had a pap test, an informed decision made 35 years ago, but incredibly, many do not believe women can reasonably decline “elective” screening.
    I was content with my near zero risk of cc rather than a 77% lifetime risk of referral and over-treatment.
    I’ve also, declined mammograms. (thanks to the Nordic Cochrane Institute for their informative summary)

    I believe unethical and non-evidence based screening is one of the greatest threats to our health and lives. All screening should be evidence based, be independently reviewed, remain current, and focused on what’s best for women and ALWAYS respect informed consent, and yes, we can say NO.

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